Threatened fishes of the world: Chiloglanis emarginatus (Jubb & le Roux, 1969) (Mochokidae)

Abstract

Common name: Phongolo rock catlet (E), Phongolo Suierbekkie (Afrikaans). Conservation status: Rare in South Africa (South African Red Data Book-Fishes, Skelton 1987), uncommon in Zimbabwe (Bell-Cross & Minshull 1988). Identification: Small (SL = 65 mm), scaleless catlet with depressed body. Disc-shaped mouth with relatively long mandibular barbels. Mandibular teeth long, up to 8 in number, widely space, width of band 25–40% width of inside of mouth. Dorsal fin with single unserrated spine. D I + 6, A III + 8. Caudal fin emarginate. Drawing by Penny Meakin. Distribution: Found in the eastern Transvaal escarpment sections of the Komati River (Incomati system) as well as the Ngwempisi, Hlelo, Assegaai and Phongolo rivers (Phongolo system) (Kleynhans 1986). C. emerginatus is also present in the Gwai, Lower Zambezi and Pungwe rivers in Zimbabwe (Bell-Cross & Minshull 1988). Abundance: Constitutes on average 5.5% of the total catch with a frequency of occurrence of 58.8% in its preferred habitat in the Incomati system. It is more common in the Phongolo system, constituting 12.1% of the total catch and having a frequency of occurrence of 75.9%. Habitat and ecology: Occurs at an altitude of 900–1200 m above sea level. This catlet has a preference for flowing water in runs, riffles and rapids (flow speed = 0.18–0.70 m sec, width = 2–5 m, depth = 0.2–0.4 m (Kleynhans 1984). The mouth is used as a sucking disc to maintain its position in fast-flowing water. The gut length is less than the standard length and the mandibular teeth are used to scrape invertebrates from stones. Feeds on epilithic aufwuchs and small stream invertebrates, especially insect larvae, ostracods and small molluscs. Co-exists with minnows (Barbus species), yellowfishes (Barbus polylepis, B. marequensis, Varicorhinus nelspruitensis) and labeos (Labeo cylindricus and L. molybdinus), the mountain catlet Amphilius uranoscopus and other Chiloglanis species. Natural enemies may include longfin eels Anguilla mossambica. Reproduction: The Phongolo rock catlet is a serial spawner that breeds from October to April and produces a maximum of about 320 ova per season (Kleynhans 1984). It is likely to be an interstitial gravel spawner like the related Chiloglanis pretoriae (de Villiers & Hecht 1991). Threats: Fragmentation of populations, habitat alteration and flow regulation due to the construction of impoundments in both the Phongolo and Incomati systems constitute the greatest threats (Kleynhans 1984). The envisaged increase in the catchment area planted with exotic tree plantations may in future decrease water runoff and water quality in this catlet’s habitat. Water abstraction for agriculture and industrial usage may also cause habitat alterations. Conservation action: Monitoring of the population numbers of this catlet and its habitat is undertaken on a regular basis by the conservation authorities. Conservation recommendations: The minimum flow requirements for the survival of this species must be determined as it is subject to flow regulation and reductions in runoff. The conservation status in Zimbabwe should be determined. Remarks: C. emarginatus is one of several species of fishes inhabiting fast-flowing rivers in southern Africa which have restricted distributions and are threatened with extinction by habitat alterations.